Danish researchers have found that girls in the first birth cohort to receive the human papillomavirus (HPV) vaccine showed a lower degree of dysplasia. Dysplasia may eventually lead to cervical cancer.

Women born in 1993 showed a higher level of mild dysplasia than women born in 1983.

The researchers of the Faculty of Health and Medical Sciences at the University of Copenhagen (Denmark) were the first to study the vaccine’s effect on the general population. The HPV vaccine was introduced as part of the Danish childhood vaccination programme in 2009. Their conclusion is unmistakable: The HPV vaccine works.

The study, published in the International Journal of Cancer, was the first to examine the effect of the vaccine in the population at large, said Prof Elsebeth Lynge of the Department of Public Health at the University of Copenhagen.

It is the first study in the world to test the Gardasil-4 vaccine at a population level. The childhood vaccination programme, which includes the HPV vaccine, is targeted at the entire population. Therefore, it is important to look at the entire population and the effect of the vaccine after the first screening of women aged 23 years, said Prof Lynge. 

REDUCTION IN SEVERE DYSPLASIA

The researchers looked at the 1993 birth cohort, which was the first to be offered the vaccine. They then compared it to a 1983 birth cohort, who were not offered HPV vaccination. The two birth cohorts of women are comparable and resemble each other with regard to level of education and average age of sexual debut, among other things.

The researchers then examined the results of the women’s first cervical screening test. The 1993 birth cohort was invited to a screening test in 2016, while women born in 1983 had their first screening test in 2006, before the vaccine was marketed.

The researchers discovered a significantly reduced risk of severe dysplasia in the 1993 birth cohort compared to the 1983 birth cohort. To be precise, the risk was reduced by 40%. “This means that fewer women have to be referred to a gynaecologist for further examination and have a tissue sample taken. Eventually we also expect fewer to fall ill,” said lead author of the study, Lise Thamsborg.

The girls from the 1993 birth cohort were 15 years old when they received the vaccine. The researchers expect the effect to be even more pronounced today, where girls are offered the vaccine at an early age already, because fewer girls become sexually active at that age, said Thamsborg.

The study also found that women born in 1993 showed a higher level of mild dysplasia than the women born in 1983. The researchers believe new technology introduced in 2006 to examine the cell samples that reveal cases of dysplasia may be the cause of the increase in cases of mild dysplasia.

The new technology has led to fewer inadequate samples, and the samples are of a higher quality today, explained Thamsborg.